The present invention relates to a material testing apparatus using ultrasonic testing heads. Such apparatus is useful for testing materials and structural components having non-uniform cross-sections, by employing ultrasonic sound waves. The two testing heads are movable in unison in the direction of changes in the cross-section of an item to be tested. However, it is conceivable that the relative movement between the testing heads and the item to be tested may also be accomplished by keeping the testing heads stationary and moving the material to be tested past the testing heads.
Prior art testing devices of this type are limited to testing of materials and structural components having a constant cross-section or wall thickness. Such prior art devices are available in several versions. One version comprises a single ultrasonic transmitter and ultrasonic receiver. Another version comprises several transmitter and receiver units operating independently of one another for the purpose of covering a larger scanning width. Such transmitter and receiver units are guided simultaneously over the surface of an item to be tested. In any event, these prior art systems are, as mentioned, limited to items having a constant wall thickness. Stated differently these prior art devices are not suitable for a volumetric testing of structural components having an irregular cross-sectional geometry because the output signals provided by such prior art systems do not make it possible to ascertain whether a change in the amplitude of the received signal is due to a fault in the material or due to a change in the geometry of the structural component. Such distinguishing becomes possible in the prior art only with the aid of rather involved and time consuming procedures which, for example, involve measuring the structural component either prior or after the testing, whereby with the aid of the measurements the instantaneous thickness of the structural component and its geometry along its entire length to be tested is taken into account to establish a fault limit curve. The instantaneous value of the ultrasonic amplitude passing therough the item to be tested is then compared with such fault limit curve during the interpretation of the test results.